1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus for performing a focus detection using a phase difference between two obtained pupil-divided images.
2. Description of the Related Art
In the related arts, such a technique that pupil-divided images are obtained by an image pickup element in which a plurality of photoelectric conversion units correspond to one microlens, and a phase difference between the two obtained pupil-divided images is obtained, to perform a focus detection has been known.
For example, Japanese Patent Application Laid-Open No. 2001-83407 discloses such a technique that a phase difference is obtained from pupil-divided images, to perform a focus detection, and at the same time, all signals of photoelectric conversion units corresponding to a same microlens are added together and output as a signal of one pixel. Japanese Patent Application Laid-Open No. 2001-83407 discloses such a technique that by handling the image signals in a manner similar to that mentioned in the latter technique, the image signals are made substantially identical to the image signals obtained by an array of image pickup pixels in the related art and an image for appreciation is formed by an image processing technique in the conventional art.
If any one of the divided photoelectric conversion units has reached a saturation, even when the outputs of all of the photoelectric conversion units corresponding to the same microlens are added up, an added output does not exhibit a linear characteristic due to an influence of the saturation, so that a picture quality deteriorates.
However, according to the related art disclosed in the above Patent Literature, although a permissible saturation level in an image which is finally obtained is improved and the picture quality is improved, a saturation level of a pupil-separated image before the addition is not improved. Rather than that, a deterioration of an image shape is caused by an influence of the pixel which absorbed charge leaked out from a saturated pixel, and a correlation of images at the time of obtaining a phase difference deteriorates.
That is, an adverse influence occurs in the focus detection, and then a focus detection precision deteriorates or the apparatus enters a state where the focus detection is impossible.
Since it may be resulted in that the focus detection is impossible while a good image has been obtained, such a situation that a state where the focus detection can be performed and a state where the focus detection is impossible cannot be distinguished appears, and this may confuse the user.